For SMN/WHM in a Healer /support capacity Carbuncle is the best. Unless you think that a pet costing 1/2 of what the light spirit does that provides ~22HP per tick Regen and a reliable ~400Hp AoE curaga is somehow inferior. Even spamming Healing Ruby II Carby is cheaper than the light spirit.
Carby will deal more Damage and heal more HP over time than a Light spirit all the while costing just as little, and being generally more reliable than a spirit, the bolded proves this. Of course it's better to use an avatar in any situation over spirits, that's how the job was designed. I've used spirits before on things and, it always became quickly apparent Avatars>Spirits.
My point is there's no need for "Spirit fixes", we already have stornger, more reliable, more versatile pets that could still use a boost. You're the biased one here, You say a small amount of perpetuation (19MP per minute is not insignifigant), sure they cost slightly less than the celestials when you factor in BPs, but they can't come close to them in any other regard.
For whatever reason you have decided to campaign on behalf of spirits, but honestly what would it get us if they were "fixed". SE could buff them to a point where they're closer to the avatars for nuking and would see more use, but in all seriousness it would leave us exxactly where we are now(obviously aside from people who like to play with spirits, your toys would be a little better), the job would remain as it was in both power and player perspective.
Spirits would never be more useful than Carbuncle for support role, because AoE regen and curaga(on command) are far better than maybe a Cure V or a Curaga IV, when either of these could easily be a Flash. I don't diss Spirit fixes out of ignorance, I diss them because a fix to them would only ever be a side grade, I want SE to spend time fixing things that both need to be fixed and will make the job more useful and better.
Making Spirits better buffers does nothing, because Avatars are already better buffers.
Making Spirits better nukers does nothing, because Avatars are already better nukers.
Making Spirits better Healers does nothing, because Avatars are already better Healers.
Making Spirits better DD/tanks does nothing, because Avatars are already better DD/tanks.
It makes far more sense to buff the more powerful pet, since the job needs a power boost anyway, thats's the only reason I'm against Spirits getting an update.